The present application claims priority to Japanese Application No. P2000-081577 filed Mar. 6, 2000 which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a nonaqueous-electrolyte secondary battery and a method of manufacturing the same, more particularly, to a lithium ion battery such as a lithium ion polymer secondary battery having a gel-type or plasticizing macromolecular electrolyte layer.
2. Description of the Related Art
In recent years, accompanying by a situation that portable small electric equipment such as small, lightweight mobile phones, or portable computers, has been popularized, secondary batteries having small, reliable output characteristics and capable of longtime-use by re-charging many times such as nickel-cadmium batteries, nickel-metal hydride batteries and lithium ion batteries have been studied and developed vastly as an electric source for supplying electric power to drive the electric equipment.
Among the secondary batteries, the lithium ion secondary battery has characteristics capable of outputting stable electric power despite its being small, lightweight and thin in size, and the battery has been studied and developed for the purpose of being employed as a foldable secondary battery by taking advantage of suitable structural characteristics for its thin size. For realizing a thinner size or a foldable shape as described above, it is suggested that a technique employ a gel-type electrolyte including plasticizer, to achieve flexibility, and a technique which employs macromolecular solid electrolyte, in which a lithium salt is dissolved in a macromolecular material, is used.
With a gel-type electrolyte or macromolecular solid electrolyte, excellent characteristics as a so-called dry cell, which is free of leakage unlike the case of using liquid-type electrolyte. However, there is a tendency such that enough electrical contact between positive and negative electrodes, can not be attained by only laminating the positive and negative electrodes and electrolyte corresponding to those electrodes. This is attributed to the reason that the gel-type, or macromolecular solid electrolyte does not have flowability the same as the liquid-type electrolyte do, so that the electrolyte and the electrodes does not contact hermetically.
In the case that a satisfactory electrical contact between the electrodes and the electrolyte can not be achieved, contact resistance inside the battery increases, thereby increasing electrical loss, which is undesirable for battery characteristics. In the case that a sufficient contact area between the electrolyte and the electrodes can not be achieved, desired ion mobility can not be gained therebetween, which decreases battery capacity less than the ordinal capacity. Accordingly, in the lithium ion battery employing the gel-type electrolyte or the macromolecular solid electrolyte as the electrolyte, it is preferable that electrolyte layers and active material layers of the electrodes contact hermetically in order to realize excellent electrical contact, which reduces the inside resistance to a minimum, and obtains the best battery capacity.
For obtaining excellent electrical contact between the electrolyte layers and the active material layers of the electrodes, it is suggested that a technique is used for changing parts where the electrolyte layers and the active material layers do not contact, or where the electrolyte layers and the active material layers do not contact partly, such that desirable contact is achieved by applying pressure from the outside, when laminating the electrolyte layers and the active material layers of the electrodes in order to form a laminating structure comprising contents inside the battery.
An invention using positive mixed materials with doped macromolecular solid electrolyte to positive electrode active layers, is suggested in Laid Open JP. No. Hei 2 (1990)-40867, for instance. This is a technique such that part of a macromolecular solid electrolyte is mixed with the positive electrode active material layers, which improves electrical contact between the macromolecular solid electrolyte and the positive electrode active material layers. However, in the case that such technique is employed for improving contact from the chemical point of view, if a satisfactory structural (physical) contact between the electrolyte layers and the electrodes is not achieved, electrical contact therebetween tends to be poor. For this reason, pressure is desirable to be applied to the laminating structure from the outside in order to gain sufficient structural contact.
Recently, as for an appropriate battery for cellular phones, portable computers and portable game machines, which has been popularized dramatically, a thin lithium ion battery has been noticed. For realizing the best appropriate thin lithium ion battery for this use, it is suggested that a structure is made in a manner that film-like electrolyte or foil-like electrodes and so on are laminated to form a laminating structure inside the battery, or are further rolled and compressed, and accommodated into film-like or thin-board like package members.
In the above-mentioned method, however, when the electrolyte layers and the electrodes are laminated and is applied pressure from the outside, a position exposed toward the outside without being covered with the electrolyte layers at an end of either the positive electrode or the negative electrode is pressurized or folded with pressure generated at this moment,to contact the other electrode, which causes short circuit between both electrodes.
Particularly, in the thin lithium ion battery, when a user adds strong force in order to put the battery into the main body of electrical equipment after manufacturing, or drops, or applies pressure to the battery, pressure is likely to be applied to the laminating structure of the battery, and in the case of the foldable thin battery, pressure attributed to that folded shape is applied to the laminating structure. As a result of this, in ends of the electrodes, specifically, parts exposed toward the outside without being covered with the electrolyte layers, contact the other electrode, thereby causing a short circuit between both electrodes.
In addition, in the lithium ion battery including the gel-type electrolyte layer, which has high flowability and poor strength, inside the laminating structure, when pressure is applied to the laminating structure from the outside, the gel-type electrolyte layer is likely to be deformed physically, thereby the ends of one electrode tends to contact the other electrode.
With the reason that excellent throughput achieves cost reduction, the positive electrode, the negative electrode and the lead electrode are stamped out (a cutting process) with a metal mold and so on, however, a protrusion such as cutting burr or curling is likely to occur in cutting ends thereon. In the case that such a protrusion occurs in one electrode, when manufacturing or using the battery, the protrusion contacts the other electrode, thereby causing a short circuit.
As another case, internal stress is generated in the electrolyte or the electrodes, which changes positions of the ends of the electrode due to seclusion change or temperature variation, thereby causing a short circuit between the both electrodes.
In the case of instigating a short circuit between both electrodes as mentioned above, effective electromotive force or battery capability of the battery seriously decreases, and much worse, no electric power output results.
The invention has been achieved in consideration of the above problems and its object is to provide a lithium ion battery capable of preventing a short circuit between both electrodes when manufacturing or using the battery as a product, and a method of manufacturing the same.
A nonaqueous-electrolyte secondary battery according to the present invention includes a laminating structure, in which a gel-type or plastic electrolyte layer, a positive electrode, and a negative electrode are laminated, and a covering member having insulation for covering one electrode opposed to a position exposed toward the outside at least from the electrolyte layer in the other electrode in an end of at least either one of the positive electrode and the negative electrode.
A nonaqueous-electrolyte secondary battery according to the present invention comprises a laminating structure, in which a gel-type or plastic electrolyte layer, a positive electrode, and a negative electrode are laminated, and a covering member having insulation and physical strength for covering one electrode opposed to a position exposed toward the outside at least from the electrolyte layer in the other electrode in an end of at least either one of the positive electrode and the negative electrode even if pressure is applied to the laminating structure.
In a case that the above-mentioned nonaqueous-electrolyte secondary battery is a solid electrolyte battery, or gel-type electrolyte, as a macromolecule material employed for macromolecular solid electrolyte, silicon gel, acryl gel, acrylonitrite gel, polyphosphazen denatured polymer, polyethylene oxide, polypropylene oxide, and composite polymer of the above-mentioned materials, cross-linked polymer of the above-mentioned materials, and a denatured polymer of these materials can be employed; as for a fluorine polymer, for example, polyvinylidenefluoride, poly(vinylidenefluoride-co-hexafluoropropylene), poly(vinylidenefluoride-co-tetrafluoroethylene) and mixture of these materials can be employed. Various materials can be also employed as the same as the above-mentioned materials.
For a solid electrolyte, or gel-type electrolyte laminated on a positive electrode active layer, or a negative electrode active layer, the following processes make preferable materials. First, a solution comprising a macromolecular compound, an electrolyte salt, and a solvent, is impregnated into the positive electrode active material, or the negative electrode active material, and solvents removed, and is solidified. A solid electrolyte or gel-type electrolyte laminated on the positive electrode active layer, or the negative electrode active layer is impregnated into the positive electrode active layer, or the negative electrode active layer, and solidifies. In the case of cross-linked materials, after the above-mentioned process, light or heat is applied to conduct cross-liking to solidify the materials.
A gel-type electrolyte is made of a plasticizer including a lithium salt and a matrix macromolecule in the range of equal to or more than 2% by weight and equal or less than 3% by weight. At this moment, esters, ethers, and carbonic acid esters can be employed independently, or as one component of the plasticizer.
When adjusting a gel-typed electrolyte, as a matrix macromolecule gelling the above-mentioned carbonic acid esters, although various macromolecules are employed for forming a gel-type electrolyte, fluorine macromolecules such as poly(vinylidenefluoride), poly(vinylidenefluoride-co-hexafluoropropylene) are preferably employed from a reduction-oxidation stability point of view.
Macromolecular electrolyte is made of a lithium salt and a macromolecular compound, in which lithium salt is dissolved. As the macromolecular electrolyte, ether macromolecules such as polyethylene oxide and cross-linked polyethylene oxide, poly(methercrylate-ester), acrylates, fluorine macromolecules such as poly(vinylidenefluoride), poly(vinylidenefluoride-co-hexafluoropropylene) can be employed independently, or as a mixture, among the above-mentioned materials, preferably, fluorine macromolecules such as poly(vinylidenefluoride) or poly(vinylidenefluoride-co-hexafluoropropylene) can be employed from reduction-oxidation stability point of view.
As a lithium salt included in such a gel-type electrolyte or macromolecular solid electrolyte, a lithium salt used for typical electrolyte for a battery can be employed. In more detail, the following materials are considered: lithium chloride; lithium bromide; lithium iodide; chloric lithium; lithium perchlorate; lithium bromate; lithium iodate; lithium nitrate; tetrafluorolithiumborate; hexafluorophosphoriclithium; lithium acetate; bis(trifluoromethanesulfonil)imidelithium, LiASF6, LiCF3SO3, LiC(SO2CF3)3, LiAlCl4, LiSiF6. In the case of the gel-type electrolyte, preferable dissolution density of a lithium salt is in the range of 0.1 to 3.0 mol in plasticizer, more preferably, in the range of 0.5 to 2.0 mol. Additionally, the kinds of lithium salt or dissolution density of are not limited by the above-mentioned materials and dissolution density.
As a negative electrode material, a material capable of doping or un-doping lithium is preferable. As such a material, for example, a non-graphitizing carbon material or a graphite material is preferably employed. More detail, pyrocarbons, cokes (pitch coke, needle coke, petroleum coke), graphites, glassy carbons, an organic macromolecular compound calcinated material (a material such that phenolic resin, furan resin and the like are calcinated at proper temperature), carbon fiber, a carbonaceous material such as activated carbon, can be employed. As other materials, a macromolecule such as polyacetylene, polypyrrole or an oxide such as SnO2 can be employed. In a case of forming a negative electrode using such materials, well-known binders may be used.
On the other hand, a positive electrode can be formed by employing a metal oxide, metal sulfide or a specific macromolecule as a positive electrode active material depending on the battery to be achieved. Take the case where a lithium ion battery is formed, for instance, as for the positive electrode active material, transition metal chalcogen compound, ex. metal sulfide, or metal oxide including no lithium such as TiS2, MoS2, NbSe2, V2O5, or lithium complex oxide mainly including LiMO2 and the like can be employed. As a transition metal M forming lithium complex oxide, Co, Ni, Mn are preferable. LiCoO2, LiNiO2, LiNiyColxe2x80x94yO2 and the like can be considered as specific examples of such lithium complex oxide. In the formula described before, M is equal to or more than one kind of transition metal, x is a value in accord with a discharge state of the batteries, typically in the range of 0.05 to 1.10, and y is a value satisfying the formula:0 less than y less than 1. These lithium complex oxides are capable of generating high voltage, which forms the positive electrode active material having excellent characteristics in energy density. When forming a positive electrode using the positive electrode active material, well-known conducting agents or binders can be doped.
Here, as for a whole structure of the battery, several types can be considered as follows: a laminated type, which the positive electrode and the negative electrode are laminated with a solid electrolyte in-between by turns, a rolled type, which the positive electrode and the negative electrode are laminated with a solid electrolyte layer in-between, a folded type, which the positive electrode and the negative electrode are laminated with the solid electrolyte layer in-between, then folded by turns. Any type can be selected arbitrarily.
A nonaqueous-electrolyte secondary battery according to the present invention has a laminating structure in which a gel-type or plastic electrolyte layer, a positive electrode and a negative electrode are laminated, and a covering member covering a position exposed at least from the electrolyte layer toward the outside in the other electrode in an end of at least either one of the positive electrode or the negative electrode.
A nonaqueous-electrolyte secondary battery according to the present invention is a nonaqueous-electrolyte secondary battery including a laminating structure, in which a gel-type or plastic electrolyte layer, a positive electrode and a negative electrode are laminated, and includes a covering member, which covers a position on one electrode exposed at least from the electrolyte layer toward the outside in the other electrode in an end of at least either one of the positive electrode and the negative electrode, and has insulation and physical strength for electrically insulating one electrode to the other electrode, even if pressure is applied to the laminating structure.
A method of manufacturing a nonaqueous-electrolyte secondary battery according to the present invention comprises a step of covering a position on one electrode opposed to a position exposed at least from an electrolyte layer toward the outside in the other electrode in an end of at least either one of a positive electrode and a negative electrode with a covering member having insulation and physical strength for insulating one electrode to the other electrode, even if pressure is applied to the laminating structure before a step of applying pressure to the laminating structure from the outside.
A method of manufacturing a nonaqueous-electrolyte secondary battery according to the present invention includes a step of covering a position on one electrode opposed to a position exposed at least from the electrolyte layer toward the outside in the other electrode in an end of either one of the positive electrode or the negative electrode, before a step of applying pressure to the laminating structure from the outside.
In a nonaqueous-electrolyte secondary battery and a method of manufacturing the same according to the present invention, a covering member having insulation covers a position on one electrode opposed to a position exposed at least from the electrolyte layer toward the outside in the other electrode in an end of at least either one of the positive electrode and the negative electrode. The covering member having insulation covers a position on one electrode opposed to a position exposed at least from an electrolyte layer toward the outside in the other electrode in either one of the positive electrode and the negative electrode. Thereby, even if one electrode is deformed in manner of approaching the other electrode due to any causes, the covering member prevents a short circuit between both electrodes.
The covering member has insulation and physical strength for electrically insulating one electrode from the other electrode even if pressure is applied to the laminating structure, in which the electrolyte layer, the positive electrode and the negative electrode are laminated. Thereby even if the end of one electrode is deformed in a manner of approaching the other electrode seriously due to strong pressure, which is applied to the laminating structure inside the battery, the covering member can prevent an electrical short circuit between both electrodes.
Other and further objects, features and advantages of the invention will appear more fully from the following description.